Method and apparatus for diagnosis of liquid losses in pressure measuring transducers filled with pressure transmitting liquids

Abstract

A method and apparatus for diagnosis of liquid losses in pressure measuring transducers including a pressure sensor arranged in a pressure measuring chamber, and a pressure transfer structure connected to the pressure measuring chamber A sealed inner space of a separating diaphragm is composed of the inner spaces of the pressure transfer structure and the pressure measuring chamber and is filled with a pressure transmitting liquid, which, serves for transmitting pressure acting on the separating diaphragm to the pressure sensor. An apparatus for detecting liquid losses. The apparatus for detecting liquid losses includes a test element arranged in the sealed inner space. The outer volume of the test element is reducible for diagnosis of liquid losses. An evaluating unit, which serves, during diagnosis, for registering, as a function of a volume reduction of the test element, a pressure measured by the pressure sensor, and, on the basis of this pressure measured as a function of the volume reduction, for detecting whether liquid has escaped.

1. A pressure measuring transducer comprising:
 a pressure measuring chamber; a pressure sensor arranged in said pressure measuring chamber; 
 pressure transfer means connected to said pressure measuring chamber, which is sealed against external surroundings by a separating diaphragm, and on which a pressure to be measured acts externally in a measurement operation; 
 a sealed inner space, which includes the inner spaces of said pressure transfer means and said pressure measuring chamber, which is filled with a pressure transmitting liquid, and which serves in measurement operations, for transferring a pressure acting on said separating diaphragm to said pressure sensor; and 
 an apparatus for diagnosis of liquid losses, which includes, arranged in said sealed inner space, a test element, whose outer volume located in said sealed inner space is reducible for diagnosis of liquid losses, and an evaluating unit, which serves during diagnosis for registering a pressure measured by said pressure sensor as a function of volume reduction of said test element, and, on the basis of pressure measured as a function of volume reduction, detects whether liquid has escaped. 
 
     
     
       2. The pressure measuring transducer as claimed in  claim 1 , wherein:
 maximum achievable volume reduction of said test element is so selected as a function of a liquid volume contained between said separating diaphragm and its diaphragm bed in the unloaded state, that said separating diaphragm lies against its diaphragm bed, when said test element assumes a minimum volume. 
 
     
     
       3. The pressure measuring transducer as claimed in  claim 1 , wherein:
 said test element contains a piezoelectric element, whose volume is reducible by applying an electrical voltage. 
 
     
     
       4. The pressure measuring transducer as claimed in  claim 1 , wherein:
 said test element is a micromechanical bellows. 
 
     
     
       5. The pressure measuring transducer as claimed in  claim 1 , wherein:
 said test element includes a movable piston. 
 
     
     
       6. A method for diagnosis of liquid losses of a pressure measuring transducer including: a pressure measuring chamber; a pressure sensor means;
 an apparatus for diagnosis of liquid losses including a test element; and an evaluation unit, the method, comprising the steps of: 
 reducing the volume of the test element, until either a non-linear falling off of the measured pressure occurs, or until an upper limit for volume reduction is reached; 
 upon occurrence of a non-linear decrease, a volume reduction associated therewith is compared with a reference value recorded in the case of intact pressure measuring transducer, and 
 on occasion, occurring liquid loss is quantified on the basis of a difference between the associated volume reduction and the reference value. 
 
     
     
       7. The method as claimed in  claim 6 , wherein:
 the diagnoses are reoccurringly executed; 
 liquid losses occurring, on occasion, are ascertained as a function of time; and 
 on the basis of liquid losses as a function of time, predictions are made concerning reliability of the measuring transducer, its life expectancy and/or a maintenance schedule or need for replacement is derived. 
 
     
     
       8. The method for diagnosis of liquid losses of a pressure measuring transducer as claimed in  claim 6 , wherein:
 the volume of the test element is reduced to a test volume, the associated pressure measured with the pressure sensor is registered, and compared with a predetermined reference pressure; and 
 based on such comparison, it is detected, whether a liquid loss is present. 
 
     
     
       9. The method for diagnosis of liquid losses of a pressure measuring transducer as claimed in  claim 8 , wherein:
 the measured pressure is compared with a reference value; and 
 the evaluating unit diagnoses a liquid loss, when the measured pressure is smaller than the reference value. 
 
     
     
       10. The method for diagnosis of liquid losses of a pressure measuring transducer as claimed in  claim 9 , wherein:
 a diagnosed liquid loss is quantified on the basis of difference between the measured pressure and the reference value. 
 
     
     
       11. The method for diagnosis of liquid losses of a pressure measuring transducer as claimed in  claim 8 , wherein:
 the measured pressure is compared with a reference value; and 
 the evaluating unit diagnoses damage leading to pressure equalization with the surroundings, when the measured pressure is larger than the reference value.